1. Field of the Invention
The present invention relates to beta-adrenergic receptor agonists and assay methods and compositions.
2. Description of the Prior Art
Beta-adrenergic receptors are widely distributed throughout the body and mediate a variety of important physiological responses. Under normal conditions, these receptors are activated by the naturally occurring catecholamines norepinephrine, released from adrenergic nerves and epinephrine which is released from the adrenal gland. Epinephrine and several synthetic beta-agonists are presently used clinically.
The beta-adrenergic receptor appears to exist in 2 subtypes, the distribution of which varies from tissue to tissue. For example, beta-1 receptors are located in the heart whereas beta-2-receptors are located on pulmonary and vascular smooth muscle. This discovery has lead to the introduction of a number of clinically useful beta-agonists and antagonists selective for one of the subtypes.
Over the past few years, a major effort has been underway in the study of adrenergic receptors. Areas of focus have included beta-receptor regulation, mechanism of receptor coupling to cellular or tissue responses, receptor desensitization and receptor turnover [Stiles et al, Physiol. Rev., Vol. 64, pp. 661-743 (1984); Maisel et al, Biochem. Pharmacol., Vol. 36, pp. 1-6 (1987)]. These studies have been made possible due to the development of radiolabeled, potent and reversible beta-receptor antagonists for directly measuring the receptor. More recently, there have been developed some irreversible beta-receptor antagonists to probe the receptor both in vitro and in vivo [Atlas et al, Proc. Natl. Acad. Sci., U.S.A., Vol. 73, pp. 1921-1925 (1976); Baker et al, J. Pharmacol. Exp. Ther., Vol. 220, pp. 247-251 (1982); Homburger et al, Arch. Pharmacol., Vol. 328, pp. 279-286 (1985)]. However, it is well known that beta-agonists induce receptor alterations related to their ability to produce responses, which antagonists do not [Abramson et al, Biochem. Pharmacol., Vol. 33, pp. 869-875 (1984)]. Thus, a major research focus has been to investigate the interaction of agonists with the receptor. To date, most agonist-receptor interaction studies have been performed indirectly by competing unlabeled agonists for labeled antagonists. Although several catecholamines have been radiolabeled for direct receptor assays [Lefkowitz et al, Proc. Natl. Acad. Sci. U.S.A. Vol. 74, pp. 515-519 (1974); Heidenreich et al, J. Cyclic Nucleotide Res., Vol. 6, pp. 217-230 (1980); Giudicelli et al, Biochim. Biophys. Acta., Vol. 715, pp. 105-115 (1982)], these compounds are limited by their low specific radioactivities and instability.
In general, catecholamine beta-agonists are unstable (due to oxidation), have relatively low potency (as compared to antagonists) and can be radiolabeled to only low specific activities. These are also problems for many of the synthetic beta-agonists. Furthermore, the catecholamine agonists have drawbacks in the clinical situation due to instability, short duration of action and many potential side effects due to a lack of receptor specificity. There exists a need for beta-agonists that are stable, potent, capable of being radiolabeled and which have a long duration of action which is based on irreversible attachment to the receptor. Carbostyril congeners have been shown to have a high bio-potency for beta-adrenergic receptors [Yoshizaka et al, J. Med. Chem., Vol. 19, pp. 1138-1142 (1976)]. One of these derivatives, erythro-5-(1-hydroxy-2-isopropylaminobutyl)-8-hydroxycarbostyril (procaterol) has been shown to be a potent beta-2 agonist and a bronchodilator although it suffers from one or more of the disadvantages discussed above [Yoshizaki et al, J. Med. Chem., Vol. 20, pp. 1103-1104 (1977)]
Catecholamine cogeners from the class of carbostyrils, indole-2-carboxylic acid and catecholamines carrying amido groups have great biopotency. See Yoshizaki et al, J. Med. Chem., Vol. 19, p. 1138 (1976); Yoshizaki et al, J. Med. Chem., Vol. 20, p. 1103 (1977); Tamura et al, J. Med. Chem., Vol. 24, p. 634 (1981); Albrecht et al, Eur. J. Med. Chem., Vol. 20, p. 57 (1985) and Jacobson et al, J. Med. Chem., Vol. 26, p. 492 (1983)].
The chemistry of compounds of this class has received some additional recent attention. See Kaiser et al, J. Med. Chem., Vol. 18, p. 1803 (1985) and Amlaiky et al, Eur. J. Med. Chem., Vol. 19, p. 341 (1984). Substituents on the amino group comprising the alkyl-aromatic part of an anorexic phentermine, 1-phenyl-2-amino-2-methylpropane, has been proven effective in catecholamine derivatives and .beta.-blockers. See Moed et al, Recl. Trav. Chim. Pays-Bas, Vol. 74, p. 919 (1955) and Lavin et al, J. Biol. Chem., Vol. 286, p. 11944 (1981).
It is an object of the invention to provide novel, stable, potent reversible and irreversible beta-adrenergic receptor agonists which will be useful as analytical probes for studying the beta-adrenergic receptor system and as drugs acting through this system.